Solar generation capacity currently represents less than 1 percent of the nation’s power assets, but as PV costs drop, solar will inevitably become a bigger part of the mix. PV, of course, is not a single technology, but an ever-growing cluster of methods to capture solar energy, and each comes with its own set of variables, pros and cons. National Renewable Energy Laboratory (NREL) analyst Michael Woodhouse spoke with Fortnightly’s Green Utility about the current state of PV research and the ongoing effort to drive down cost.

GU: How many different photovoltaic technologies are you currently exploring at NREL?

MW: NREL is a spawning ground for a lot of PV technologies -- everything from incumbent technologies that you see in the field now, to next generation materials and systems that aren’t commercially available yet. Most products that a consumer would currently buy are made out of crystalline silicon. We have research groups working on that system. We also have groups looking at new materials for the thin-film systems, including cadmium telluride and copper indium gallium selenide, or CIGS. We have organic PV research groups. There’s one for next generation concepts, such as quantum-dot solar cells. There’s a dye-sensitized solar cell research group. So we’re looking at the whole gamut of PV technologies that you could think of, and in a lot of cases companies have sprung out of that research.

GU: Don’t some to the materials you just mentioned present sourcing problems, either because of their scarcity or geopolitical issues?

MW: Crystalline silicon, which currently accounts for 88 percent of the market, is certainly earth-abundant. All you need to make that is high quality quartz or sand. When it comes to the thin-film technologies, there are concerns about cadmium telluride, because tellurium that goes into making that presents a potential supply problem in the long term. The indium that goes into making CIGS is potential issue to look at as well. That’s not to say that materials availability is always going to be a problem for PV, because there are always alternative materials being developed. If we run into a supply problem with CIGS, for example, a good replacement technology may be copper zinc tin sulfide, or CZTS. That said, it’s still too early to say whether materials availability will be a significant problem or not.

GU: What about toxicity?

MW: Usually the one that people talk about there is cadmium telluride, because they have concerns about cadmium. A couple of points are worth noting about that: First of all, there’s more cadmium in a NiCad battery, which are all over the place, than there is in a cadmium telluride solar panel. The cadmium telluride in a solar cell is really thin -- usually something along the order of three micrometers, which is a fraction of the thickness of a human